Cellulose ester tow is known. Kirk-Othmer, Encyclopedia of Chemical Technology, 4th Edition, Vol. 5, John Wiley & Sons, New York, N.Y., 1993, p. 496-529. Cellulose acetate tow is known. Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Vol. 5, John Wiley & Sons, New York, N.Y., 1979, p. 89-117. Cellulose acetate tow impregnated with titanium dioxide pigments, either anatase or rutile, as a delustrant is known. See: Kirk-Othmer, Ibid, 3rd Edition, p. 90; and U.S. Pat. No. 4,022,632. The ideal delustering titanium dioxide pigment has a particle size ranging from 200 to 350 nm (0.2 to 0.35 microns). See: Undated publication of Kemira, Inc. entitled "The Savannah Story". These pigments are typically coated to retard their photocatalytic effect. Rabek, J. F., Mechanisms of Photophysical Processes and Photochemical Reactions in Polymers, John Wiley & Sons, New York City, N.Y., 1987, p. 585-587.
It has been proposed that anatase-type titanium dioxides can be used to accelerate the photodegradation of cellulose ester tows. See: EPO Publication No. 597,478; WO 93/24685; and U.S. Pat. No. 5,242,880. These photodegradable cellulose ester tows utilize uncoated anatases. Ibid. As a photodegradability accelerator, anatase-type titanium dioxide is better than rutile-type titanium dioxide. In EPO Publication No. 597,478, the cellulose ester tow has about 0-5% by weight of an anatase-type titanium dioxide having an average particle diameter of about 300 nm (0.3 microns), a particle size distribution of 10-1000 nm (0.01-1 micron), and specific surface area of 3 to 30 m.sup.2 /g. In WO 93/24685, the average particle size is given by reference to the exemplary photoactive anatase titanium dioxides set forth in Table 1 at page 48. Therein, three commercially available pigments are disclosed. Each is believed to have an average particle size of about 350 nm (0.35 microns). In U.S. Pat. No. 5,242,880, an oxidizable polymer such as cellulose acetate or polypropylene, is impregnated with a photoactive catalyst to increase biodegradability. The photoactive catalyst comprises an anatase-type titanium dioxide containing or coated with a salt. The salt comprises between 2-30 weight percent of the catalyst.
Fine particle, crystalline titanium dioxides (8-210 nm or 0.008-0.210 micron) are known for use as photodegradants in plastics. See: Meldrum, B. J., "Fine Particle TiO.sub.2 --A Brief Introduction", SPE 49th Annual Technical Conference Exhibits, 1991. Therein, uncoated, fine particles of titanium dioxide are loaded into polypropylene film which is then exposed to ultraviolet radiation, so to demonstrate the photodegradation effect.
There is a need for photodegradable cellulose ester tows that can minimize the littering problem associated with the disposal of spent cigarettes, having filters made from cellulose esters tows, on roadsides and the like.